fix(aws-lambda): route an omitted PlanProtocol before comparing it

examples/aws-lambda/template.yaml

@@ -266,6 +266,11 @@ Resources:
           SelectPlanProtocol:
             Type: Choice
             Choices:
+              # A comparison on a missing path is a States.Runtime error, not a non-match, so an
+              # omitted PlanProtocol has to be caught before any StringEquals rule.
+              - Variable: $.PlanProtocol
+                IsPresent: false
+                Next: !If [HasVideoFunction, WarmRender, PlanV2]
               # Only a stack with the arm64 video function has a cold x86 function to warm.
               # Without one the compared value can never match.
               - Variable: $.PlanProtocol

packages/aws-lambda/src/cdk/HyperframesRenderStack.snapshot.test.ts

@@ -185,6 +185,26 @@ describe("HyperframesRenderStack — snapshot", () => {
     }
   });
 
+  // Step Functions raises States.Runtime for a comparison on a missing path instead of moving on,
+  // so the Default branch is unreachable unless presence is checked before any comparison.
+  it("routes an omitted plan protocol before any rule compares it", () => {
+    for (const [name, definition] of [
+      ["CDK", SYNTHED.definition],
+      ["SAM", readSamDefinition()],
+    ] as const) {
+      const choices = requireRecord(definition.States.SelectPlanProtocol, "SelectPlanProtocol")
+        .Choices as Record<string, unknown>[];
+      expect({ name, first: { ...choices[0], Next: undefined } }).toEqual({
+        name,
+        first: { Variable: "$.PlanProtocol", IsPresent: false, Next: undefined },
+      });
+    }
+    expect(SYNTHED.definition.States.SelectPlanProtocol.Choices[0].Next).toBe("PlanV2");
+    const samFirst = (readSamDefinition().States.SelectPlanProtocol as Record<string, unknown>)
+      .Choices as Record<string, unknown>[];
+    expect(samFirst[0].Next).toEqual(["HasVideoFunction", "WarmRender", "PlanV2"]);
+  });
+
   it("preserves every typed non-retryable error name across the three Lambda tasks", () => {
     const { definition } = SYNTHED;
     const collected = new Set<string>();

packages/aws-lambda/src/cdk/HyperframesRenderStack.ts

@@ -443,7 +443,10 @@ export class HyperframesRenderStack extends Construct {
       error: "PLAN_PROTOCOL_UNSUPPORTED",
       cause: 'PlanProtocol must be "v2" or absent (defaults to v2).',
     });
+    // A comparison on a missing path is a States.Runtime error, not a non-match, so an omitted
+    // PlanProtocol has to be caught before the stringEquals rule.
     return new sfn.Choice(this, "SelectPlanProtocol")
+      .when(sfn.Condition.isNotPresent("$.PlanProtocol"), planV2)
       .when(sfn.Condition.stringEquals("$.PlanProtocol", "v2"), planV2)
       .when(sfn.Condition.isPresent("$.PlanProtocol"), unsupportedPlanProtocol)
       .otherwise(planV2);